Investigation on the river water polluted with acidic hot spring water

Tamagawa hot spring in Akita Prefecture gushes hot water of 1 pH hydrochloric acid at some 140 1 s⁻¹. This quantity flows into the River Tama with the result that the river has been denied use for any significant hydropower development thus far. For the purpose of mitigating the acidity of the river water, the hot spring water is carried away through channels and infiltrated into the soil of a mountainside for chemical neutralizing through seepage before flowing into the river.The following facts have been obtained by field geochemical investigation (1951–1963). The neutralization effect following the injection of hot-spring water into the soil is about 80 per cent, the larger part of which effect is due to the function of dissolution of Al³⁺; the pH values of the water in the reservoir of Yoroibata dam to be constructed downstream of the river do not exceed 5; and even in the absence of hot-spring water injection treatment there is acidity reduction due to the alkalinity of the tributary waters as well as due to the dissolution of river-bed components by the acid during seepage.